Writing EXIF data (and how to define the side of the photo)

Anyone had luck writing EXIF data in photos? Reading EXIF data are fairly easy, as demonstrated by "photobomber. Writing EXIF data seems to be more painful, however.

In particular, I'm trying the face value of the photo. I found mention on the web page of its existence in EXIF, with the code:

0 x 4746

That said, when I check the exif - tag.h, apparently not be listed.

It is clear to me that this is a deal breaker or not. The tags are listed in the exif - tag.h the only ones that can be used? Or are they simply definitions of convenience tag codes most commonly used?

Thank you

Daniel

Incase others are reading this in the future and ask yourself how: my conclusion is that the best way to define metadata such as:

-Photo rating

-Tags

-Description

... does NOT use EXIF. On the contrary, it seems that XMP is a much better choice:

http://en.Wikipedia.org/wiki/Extensible_Metadata_Platform

Ideally, BB10 comes with the XMP library, and it can be easily added to your project. (right-click on the project node in "Project Explorer", go to the context menu item 'Configure', then 'add the library')

Here's the code I added bo my main.cpp:

//-----------------------------------------------------------------------------
// XMP
//-----------------------------------------------------------------------------

// Must be defined to instantiate template classes
#define TXMP_STRING_TYPE std::string

// Must be defined to give access to XMPFiles
#define XMP_INCLUDE_XMPFILES 1

#define UNIX_ENV 1

#include "xmp/XMP.incl_cpp"
#include "xmp/XMP.hpp"

#include 
#include 

using namespace std;

//-----------------------------------------------------------------------------

... and here's what I added to the .h file that I wanted to use XMP in: (it does not include the XMP.incl_cpp at the top of the notice)

//-----------------------------------------------------------------------------
// XMP
//-----------------------------------------------------------------------------

#define TXMP_STRING_TYPE std::string
#define XMP_INCLUDE_XMPFILES 1
#define UNIX_ENV 1

#include "xmp/XMP.hpp"

#include 
#include 

using namespace std;

//-----------------------------------------------------------------------------

And finally, here's a big copy and paste part of the key code that I adapted to the code example in the XMP SDK I downloaded separately for read/write some common tags. Feel free to use this code in your own applications, or to adapt it, if that's helpful.

int ImageViewContainer::xmpWrite()
{
    qDebug() << "xmpWrite()";

    string filename = file.toStdString();

    if (!SXMPMeta::Initialize())
    {
        qDebug() << "XMP: An error occurred initializing XMP.";
        return -1;
    }

    XMP_OptionBits options = 0;

    #if UNIX_ENV
        options |= kXMPFiles_ServerMode;
    #endif

    if (!SXMPFiles::Initialize(options))
    {
        qDebug() << "XMP: An error occurred initializing SXMPFiles.";
        return -1;
    }

    try
    {
        // Try using the smart handler.
        XMP_OptionBits opts = kXMPFiles_OpenForUpdate | kXMPFiles_OpenUseSmartHandler;

        bool ok;
        SXMPFiles myFile;

        // Open the file.
        ok = myFile.OpenFile(filename, kXMP_UnknownFile, opts);
        if (!ok)
        {
            qDebug() << "XMP: No smart handler available for " + file + ". Trying packet scanning.";

            // Now try using packet scanning.
            opts = kXMPFiles_OpenForUpdate | kXMPFiles_OpenUsePacketScanning;
            ok = myFile.OpenFile(filename, kXMP_UnknownFile, opts);
        }

        // If the file is open then read the metadata.
        if (ok)
        {
            qDebug() << "XMP: Opened: " << file;

            // Create the xmp object and get the xmp data.
            SXMPMeta meta;
            myFile.GetXMP(&meta);

            // Should we be doing this?
            meta.SetProperty(kXMP_NS_XMP, "CreatorTool", "Updated by PhotoStar", 0);

            int ratingToSet = rating;
            if (ratingToSet == -1) { ratingToSet = 0; }
            meta.SetProperty(kXMP_NS_XMP, "Rating", QString::number(ratingToSet).toStdString(), 0);

            // Required before we can call other functions that refer to this namespace
            // without getting an exception.
            std::string tmp;
            meta.RegisterNamespace("http://ns.microsoft.com/photo/1.0/", "MicrosoftPhoto", &tmp);

            if (ratingToSet == -1)
            {
                meta.DeleteProperty("http://ns.microsoft.com/photo/1.0/", "Rating");
            }
            else
            {
                int microsoftRating;

                // Mapping:
                // xmp:Rating=1 -> MicrosoftPhoto:Rating=1
                // xmp:Rating=2 -> MicrosoftPhoto:Rating=25
                // xmp:Rating=3 -> MicrosoftPhoto:Rating=50
                // xmp:Rating=4 -> MicrosoftPhoto:Rating=75
                // xmp:Rating=5 -> MicrosoftPhoto:Rating=100

                if (ratingToSet == 1)
                {
                    microsoftRating = 1;
                }
                else
                {
                    microsoftRating = (ratingToSet - 1) * 25;
                }

                qDebug() << "MicrosoftPhoto:Rating: " << QString::number(microsoftRating);
                meta.SetProperty("http://ns.microsoft.com/photo/1.0/", "Rating", QString::number(microsoftRating).toStdString(), 0);
            }

            // Delete old tags. (?)
            meta.DeleteProperty(kXMP_NS_DC, "subject");

            // Tags
            for (int i = 0; i < tags.size(); ++i)
            {
                string value = tags[i].toStdString();
                meta.AppendArrayItem(kXMP_NS_DC, "subject", kXMP_PropArrayIsOrdered, value, 0);
                //meta.SetArrayItem(kXMP_NS_DC, "subject", i + 1, value, 0);
            }

            meta.SetLocalizedText(kXMP_NS_XMP, "Description", "en", "en-US", description.toStdString(), NULL);

            // Update the Metadata Date
            XMP_DateTime updatedTime;

            // Get the current time. This is a UTC time automatically adjusted for the local time.
            SXMPUtils::CurrentDateTime(&updatedTime);
            //if (meta.DoesPropertyExist(kXMP_NS_XMP, "MetadataDate"))
            //{
                meta.SetProperty_Date(kXMP_NS_XMP, "MetadataDate", updatedTime, 0);
            //}

            // Now update alt-text properties
            //meta.SetLocalizedText(kXMP_NS_DC, "title", "en", "en-US", "Kind of pretty");

            // For debugging
            if (false)
            {
                // Serialize the packet and write the buffer to a file.
                // Let the padding be computed and use the default linefeed and indents without limits.
                string metaBuffer;
                meta.SerializeToBuffer(&metaBuffer, 0, 0, "", "", 0);

                //qDebug() << QString::fromStdString(metaBuffer);

                // Write the packet to a file as RDF
                writeRDFToFile(&metaBuffer, filename + "_XMP_RDF.txt");
            }

            // Check we can put the XMP packet back into the file.
            if (myFile.CanPutXMP(meta))
            {
                // If so then update the file with the modified XMP.
                myFile.PutXMP(meta);
            }
            else
            {
                // Silent for now. TODO: Should this be indicated in
                // the UI somehow?
                qDebug() << "XMP: Can't write to file.";
            }

            // Close the SXMPFile. This *must* be called. The XMP is not actually written and the
            // disk file is not closed until this call is made.
            myFile.CloseFile();
        }
        else
        {
            qDebug() << "XMP: Unable to open " << file;
        }
    }
    catch(XMP_Error & e)
    {
        qDebug() << "XMP ERROR: " << QString::fromStdString(e.GetErrMsg());
    }

    // Terminate the toolkit
    SXMPFiles::Terminate();
    SXMPMeta::Terminate();

    return 0;
}

int ImageViewContainer::xmpRead()
{
    qDebug() << "xmpRead()";

    string filename = file.toStdString();

    if (!SXMPMeta::Initialize())
    {
        qDebug() << "XMP: An error occurred initializing XMP.";
        return -1;
    }

    XMP_OptionBits options = 0;

    #if UNIX_ENV
        options |= kXMPFiles_ServerMode;
    #endif

    if (!SXMPFiles::Initialize(options))
    {
        qDebug() << "XMP: An error occurred initializing SXMPFiles.";
        return -1;
    }

    try
    {
        // Try using the smart handler.
        XMP_OptionBits opts = kXMPFiles_OpenForRead | kXMPFiles_OpenUseSmartHandler;

        bool ok;
        SXMPFiles myFile;

        // Open the file.
        ok = myFile.OpenFile(filename, kXMP_UnknownFile, opts);
        if (!ok)
        {
            qDebug() << "XMP: No smart handler available for " + file + ". Trying packet scanning.";

            // Now try using packet scanning.
            opts = kXMPFiles_OpenForUpdate | kXMPFiles_OpenUsePacketScanning;
            ok = myFile.OpenFile(filename, kXMP_UnknownFile, opts);
        }

        // If the file is open then read the metadata.
        if (ok)
        {
            qDebug() << "XMP: Opened: " << file;

            // Create the xmp object and get the xmp data.
            SXMPMeta meta;
            myFile.GetXMP(&meta);

            bool exists;

            // Stores the value for the property.
            string value;

            // XMP Rating
            exists = meta.GetProperty(kXMP_NS_XMP, "Rating", &value, NULL);
            if (exists)
            {
                rating = QString::fromStdString(value).toInt(&ok);
                if (!ok)
                {
                    rating = -1;
                }
            }
            else
            {
                rating = -1;
            }

            // Microsoft Rating (only look for this if xmp:Rating is missing)
            if (rating == -1)
            {
                // Required before we can call other functions that refer to this namespace
                // without getting an exception.
                std::string tmp;
                meta.RegisterNamespace("http://ns.microsoft.com/photo/1.0/", "MicrosoftPhoto", &tmp);

                exists = meta.GetProperty("http://ns.microsoft.com/photo/1.0/", "MicrosoftPhoto:Rating", &value, NULL);
                //exists = meta.GetProperty(kXMP_NS_XMP, "Rating", &value, NULL);
                if (exists)
                {
                    rating = QString::fromStdString(value).toInt(&ok);
                    if (!ok)
                    {
                        rating = -1;
                    }
                    else
                    {
                        // The Microsoft rating is 0, 25, 50, 75, 100.
                        rating /= 25;
                    }
                }
                else
                {
                    rating = -1;
                }
            }

            value.clear();

            qDebug() << "XMP Rating: " << rating;

            // Tags
            tags.clear();
            int arraySize = meta.CountArrayItems(kXMP_NS_DC, "subject");
            for (int i = 1; i <= arraySize; i++)
            {
                meta.GetArrayItem(kXMP_NS_DC, "subject", i, &value, 0);
                qDebug() << "XMP Tag[" << i << "]: " << QString::fromStdString(value);
                tags.append(QString::fromStdString(value));
            }

            value.clear();

            // Description
            meta.GetLocalizedText(kXMP_NS_XMP, "Description", "en", "en-US", NULL, &value, NULL);
            description = QString::fromStdString(value);
            qDebug() << "XMP Description: " << description;

            timestamp = QDateTime();
            XMP_DateTime updatedTime;
            // Get the current time. This is a UTC time automatically adjusted for the local time.
            SXMPUtils::CurrentDateTime(&updatedTime);
            if (meta.DoesPropertyExist(kXMP_NS_XMP, "MetadataDate"))
            {
                meta.GetProperty_Date(kXMP_NS_XMP, "MetadataDate", &updatedTime, 0);
                if (updatedTime.hasDate)
                {
                    if (updatedTime.hasTime)
                    {
                        timestamp = QDateTime(QDate(updatedTime.year, updatedTime.month, updatedTime.day), QTime(updatedTime.hour, updatedTime.minute, updatedTime.second));
                    }
                    else
                    {
                        timestamp = QDateTime(QDate(updatedTime.year, updatedTime.month, updatedTime.day), QTime(0, 0, 0));
                    }
                }
            }

            // Close the SXMPFile. The resource file is already closed if it was
            // opened as read only but this call must still be made.
            myFile.CloseFile();
        }
        else
        {
            qDebug() << "XMP: Unable to open " << file;
        }
    }
    catch(XMP_Error & e)
    {
        qDebug() << "XMP ERROR: " << QString::fromStdString(e.GetErrMsg());
    }

    // Terminate the toolkit
    SXMPFiles::Terminate();
    SXMPMeta::Terminate();

    return 0;
}

Note that the code above makes use of some class member variables:

    int rating;
    QList tags;
    QString description;
    QDateTime timestamp;

One final note: there is a code that deals with the MicrosoftPhoto:Rating XMP tag. It's because I'm on Windows and I noticed that if you click on a photo in Windows Explorer, it allows you to display/change some meta (such as star ratings) data directly in Explorer. When you do so, it sets the MicrosoftPhoto:Rating tag (as well as the tag xmp:Rating, I believe). Once, he put that, if your application updates the xmp:Rating tag but don't update the MicrosoftPhoto:Rating tag and the file returns on Windows, then he continues to use the old notation before your update app. (he seems to ignore xmp:Rating if MicrosoftPhoto:Rating is present)

Tags: BlackBerry Developers

Writing EXIF data (and how to define the side of the photo)

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